The invention relates to contact means for conductor foils.
There is known a contact element of the Dupont Company serving to enable to make a contact with the conductor path of the conductor foil at any location, in order, for example, to connect a cable to the conductor path or to make a connection to a conductor path of an other conductor foil. In order to make a contact with the conductor path of the conductor foil, a contact piece provided with holding clips is placed on the conductor foil and is subsequently pressed onto the conductor foil such that the holding clips cut through the conductor foil and the conductor path and exit on the rear face. Finally, the holding clips are crimped over outwards such that the contact piece is fixedly connected to the conductor foil. Thus, the contact with the conductor path is attained by means of the holding clips which are pressed against the conductor paths.
The known contact means presents the disadvantage that the quality of the attained contact gradually deteriorates, because the synthetic material of the conductor foil slowly yields under the pressure applied by the holding clips. Thus, the contact force acting at the contact location is gradually reduced such that the gas tightness of the contact location, on the one hand, and the required contact pressure at the contact location, on the other hand, are not reliably guaranteed.
From WO 98/11629 there is known a contact element provided with a spring clip. The spring clip presents a spherical pressure surface and the contact element is provided with a circular recess. The contact with the conductor path of the conductor foil is attained in the region of the circular pressure line between the edge the recess and the pressure surface.
It is therefore the object of the invention to provide a contact means for conductor foils which guarantees the quality of the contact even for very long periods of time and which at the same time is suitable for large current intensities.
To this end according to the invention there is provided a contact means for conductor foils which comprises at least one conductor path, the contact means comprising a pressure element which is provided with a projection presenting a continuous pressure surface, and a counter pressure element provided with a recess the contour of which is adapted to the shape of the pressure surface, the projection being prestressed or biased elastically against the counter pressure element such that a conductor foil to be contacted is clamped between the pressure surface and the edge of the recess. The invention basically relies on the combination of a line contact of the conductor path and of an elastic prestress or elastic bias. The line contact ensures that the contact is attained along precisely defined regions of the conductor path. This is very important because of the fact that a surface pressure at the conductor path which is considered to be advantageous for the respective application can be maintained only if the contact area is known. The elastic prestress of the projection against the edge of the recess in the counter pressure element serves to maintain the contact force once adjusted even if the conductor foil gradually begins to yield due to the applied contact force.
Preferably the pressure surface has the shape of pyramid or a truncated pyramid and the recess has a polygonal shape adapted to the cross-section of the pyramid. Alternatively, the pressure surface has the shape of an ellipsoid or of a part of an ellipsoid and the recess is shaped elliptical. The advantage of this shaping is that a comparatively long line contact between the edge of the recess and the pressure surface is attained with respect to the xe2x80x9cfootingxe2x80x9d of the recess, which is in particular longer than with a circular recess. In view of the fact that most contacts are rectangular there can be attained with the same contact width a contact area which is much more larger than with a circular recess by using an elliptical or a long rectangular recess.
However, alternatively, it is conceivable to use the circular recess already known in the prior art along with a spherical pressure surface; in this case, however, the above mentioned advantage of an optimal utilization of the area is not attained.
According to an embodiment of the invention the pressure element and the counter pressure element consist of sheet metal, the projection being formed by an embossing on the pressure element and the recess being formed by an opening punched in the counter pressure element. This embodiment results in very small manufacturing costs for the connection contact means.
Preferably the pressure element and the counter pressure element are attached to each other by holding clips which are arranged on both sides of the projection and of the recess such that the inherent material elasticity of both elements prestresses the projection against the recess. The holding clips allow to attach both elements to each other by comparatively simple means. Preferably the holding clips are arranged such that they automatically cut through the conductor foils so that corresponding openings are not to be pre-punched.
The pressure element and the counter pressure element may be integrally formed. Thereby the assembly is facilitated, since only one piece has to be manipulated. For assembly preferably one of both elements is arranged on the conductor foil and subsequently the other element is bent by 180xc2x0 such that it is folded back onto the conductor foil and lies opposite to the other element. The bending region in which the pressure element is connected to the counter pressure element is preferably formed at the end of a contact clip of the contact means, said contact clip protruding from the conductor foil and allowing the contact of the contact means by means of a cable lug, for instance.
According to a second embodiment the pressure element is a resilient clip being attached to an insulating casing and having a free end at which the projection is formed, and that the counter pressure element is a contact tongue in which the recess is punched out. In this embodiment the contact means is formed in the nature of a connector having a casing which can be gripped very good and which can be inserted into an associated connection.
Preferably the resilient clip is provided with a retention nose which can cooperate with a retention recess in the contact tongue. In this manner a tension relief is formed.
Advantageously the casing is provided with a recess for a leaf spring which can be inserted afterwards and which prestresses the projection against the recess. This allows to insert the conductor foil into the contact freely at first until it is placed in its correct position. Only then a tension force is produced by inserting the leaf spring, said force providing the required contact force, on the one hand, and clamps the conductor foil in the casing, on the other hand. By this functional and constructive separation of the pressure surface from the spring action the contact force can be adapted to the respective suitable contact force independently of the shape of the contact tongue by selecting a suitable leaf spring.
Independently of the respective embodiment the pressure surface and the recess are preferably dimensioned such that the length of the edge of the recess is approximately equal to the width of the conductor path to be contacted. If, for example, a square recess is used its width is selected such that it lies in the order of nearly a quarter of the width of the conductor path to be contacted. Such dimensioning has proved to be advantageous for the current carrying in the junction region between the contact and the conductor path.
Advantageous embodiments of the invention appear from the sub-claims.